Alloy for high temperature applications



United States Patent ALLOY FOR HIGH TEMPERATURE APPLICATIONS Falih N. Darmara, New Hartford, N. Y., assignor to Utica Drop Forge & Tool Corporation, Utica, N. Y., a corporation of New York No Drawing. Application August 5, 1954, Serial No. 448,147

8 Claims. (Cl. 75-171) The invention relates to alloys for use at high temperatures, and to methods of preparing such alloys. It relates more particularly to alloys containing substantial amounts of nickel, cobalt, and chromium, and lesser but effective amounts of aluminum, titanium and molybdenum. Other alloying elements may be present, such as tungsten, zirconium, iron, silicon or manganese.

The significant feature of the invention is the discovery that both aluminum and titanium may be simultaneously present, in substantial amounts, and with remarkably improved effect on the high temperature properties, especially if the alloy is prepared by melting in a vacuum melting furnace. Heretofore alloys of this nature, and containing both aluminum and titanium in substantial amounts, developed undesirable inclusions in the metal as a result, i believe, of reaction of the aluminum and titanium with the atmosphere, or with the slag or other unwanted inclusions in the melt, during the melting process. The present invention produces an alloy free from such impurities, and, as will appear, the resulting hightemperature properties are considerably improved over those previously obtainable.

There is a very pressing demand for high-melting point alloys which retain high strength at elevated temperatures. One such adaptation is exemplified by the gas turbine blades for jet engines. In this industry the trend has been towards the development of engines with higher and higher thrust. One conventional way of obtaining higher thrust without loss of efficiency, or even with improved efiiciency, is to raise the temperature of the gases impinging on the turbine blades. The extremely high temperature imposes exacting strength requirements on the turbine blade material because of course all metals and alloys deteriorate in physical properties in the upper temperature ranges. It may be stated, as a consequence, that the further development of higher thrust engines awaits the development of new alloys having physical properties, and particularly tensile strength and yield strength, adequate to sustain applied stresses at higher and higher temperatures.

An object of the present invention is to develop a suitable alloy for high temperature applications, having at elevated temperatures physical properties superior to those previously attainable by commercially feasible methods of manufacture.

A further object of the invention is to provide an alloy as defined in the last preceding paragraph, in which the alloying elements have been combined under conditions conducive to the development of exceptional physical properties at high temperatures. 7 V V A further object of the invention is to provide an alloy consisting of a nickel-cobalt-chromium base matrix, and containing lesser but effective amounts of other constituents, but especially aluminum and titanium combined to a total amount somewhat higher than is commercially usable in an alloy of this type.

A further object of the invention is to provide an alloy as defined in the last preceding paragraph in which the melting and alloying takes place in a vacuum furnace.

Other objects and advantages will be apparent from a study of the following specification which describes the invention in greater detail.

As hereinabove indicated the basic alloying constituents are nickel, chromium, and cobalt. The chromium may be present in amount between 15.0 percent and 30.0 percent by weight, and the cobalt also between 15.0 percent and 30.0 percent by weight. The alloy may contain some iron, but not in excess of twenty percent, and some silicon and manganese, but not in excess of 0.5 percent of either. Molybdenum and tungsten can be present in a combined amount between about 1.5 percent and 10.0 percent, or either may be present individually within the same range.

The significant elements are aluminum and titanium, the aluminum between about 2.75 percent and 5.0 percent, and the titanium between about 2.5 percent and 7.5 percent. The simultaneous presence of these two elements imparts to the alloy its exceptional high temperature properties.

These very favorable properties will be found to be present, to an exceptional degree, in the following more specific composition: carbon 0.10 percent maximum; sulfur 0.01 percent maximum; aluminum between 2.75 percent and 3.25 percent; titanium between 2.75 percent and 3.25 percent; molybdenum (or tungsten) between 3.5 percent and 4.5 percent; chromium between 19.0 percent and 22.0 percent; cobalt between about 14.0 percent and 16.0 percent; iron up to 5.0 percent maximum; silicon up to 0.75 percent maximum; manganese up to 0.5 percent; nickel forms the balance of the alloy disregarding impurities which may be present in minute amounts.

A useful test for determining the suitability of materials for high temperature applications is the so called stress rupture test. In this test specimens of the alloy to be tested are subjected to a continuously applied stress while the specimens are maintained at selected elevated temperatures until the specimens finally fail or rupture. The applied stress at time of rupture is calculated in pounds per square inch in the usual way, and also the percent elongation as a measure of the ductility. The significant statistic is of course the length of time the specimen withstood the stress before rupture.

A number of such tests at respectively varied temperatures will provide material for construction of a curve from which the behavior of an alloy at any applied temperature may be predicted.

To demonstrate the very favorable properties of an 1 Stress in Life in Percent Temp. in degrees F. lbs. per sq Hours Elong.

inch

For purposes of comparison, there is presented herewith a series of tests on a related composition, but with a lower aluminum content, below the composition range of the present invention. This alloy had the following Stress in Life in Percent Temp. in degrees F. lbs. per Hours Elong.

sq. inch By comparison of the above two series of tests it may be noted, for example at 1350 F. and 65,000 pounds per square inch, the alloy of the present invention stood up against the applied stress for 340.8 hours, while the comparison alloy had a life of only 111.4 hours under identical conditions. It may be further noted that at 1500 F. and 37,500 pounds per square inch the alloy of the present invention resisted rupture for 250.4 hours while the comparison alloy lasted only 61.9 hours. Finally it may be noted that at 1600 F. and 25,000 pounds per square inch the alloy of the present invention resisted rupture for 214.2 hours While under identical conditions the comparison alloy lasted only 35.4 hours.

The improvement produced by the combination of relatively high aluminum and titanium, alloyed in vacuum, is quite striking. The alloys compared herein were given standard thermal treatments of the solution, stabilizing, and aging type'.

As a result of these treatments, optimum amounts of the aluminum and titanium are dissolved and re-precipitated. The solution treatment is four hours at 1975 F. followed by air cooling. The stabilizing treatment is twenty four hours at 1550 F. followed by air cooling. The aging treatment is sixteen hours at 1400 F. followed by air cooling.

While the alloys herein described and claimed are productive of improved high temperature properties even when melted under conventional conditions, the best results are obtained when they are melted in a vacuum furnace under very low pressures in the order of five to ten microns. By a combination of the various factors including the simultaneous use of high aluminum and titanium, vacuum melting, and relatively pure materials, it has been possible to make alloys of the nature described with excellent high temperature properties and very satisfactory ductility. As heretofore noted, alloys of this type which in the past were attempted to be compounded with both high aluminum and high titanium were exceptionally dirty by reason of reaction of the aluminum and titanium with the atmosphere and the slag.

In the alloys disclosed herein an equal amount of zirconium may be substituted for some or all of the titanium while still retaining to a marked extent the advantages of the invention.

What is claimed is:

1. A nickel base alloy containing from 15.0 percent to 30.0 percent of chromium, from .0 percent to 30.0 percent of cobalt, from 2.75 percent to 5.0 percent of aluminum, from 2.5 percent to 7.5 percent of titanium, the alloy being capable of withstanding an applied stress of thirty five thousand pounds per square inch at 1500 F. for a time in excess of two hundred hours continuously, without rupture.

2. A nickel base alloy containing from 15.0 percent to 30 percent of chromium, from 15.0 percent to 30.0 percent of cobalt, from 1.5 percent to 10.0 percent of at least one metal of the group consisting of molybdenum and tungsten, and mixtures thereof, from,2.5 percent to 7.5 percent of at least one member of the group consisting of zirconium and titanium, and mixtures thereof,

and from 2.75 percent to 5.0 percent of aluminum, the alloy being capable of withstanding an applied stress of thirty five thousand pounds per square inch at 1500 F. for a time in excess of two hundred hours continuously, without rupture.

3. A nickel base alloy containing from 15.0 percent to 30.0 percent of chromium, from 15.0 percent to 30.0 percent of cobalt, from 1.5 percent to 10.0 percent of at least one metal of the group consisting of molybdenum and tungsten, and mixtures thereof, from 2.5 percent to 7.5 percent of titanium and from 2.75 percent to 5.0 percent of aluminum, the alloy being capable of withstanding an applied stress of thirty five thousand pounds per square inch at 1500 F. for a time inexcess of two hundred hours continuously, without rupture.

4. A nickel base alloy containing from 15.0 percent to 30.0 percent of chromium, from 15.0 percent to 30.0 percent of cobalt, from 1.5 percent to 10.0 percent of molybdenum, from 2.5 percent to 7.5 percent of titanium and from 2.75 percent to 5.0 percent of aluminum, the alloy being capable of withstanding an applied stress of thirty five thousand pounds per square inch at 1500 F. for a time in excess of two hundred hours continuously, without rupture.

5. A nickel base alloy containing from 15.0 percent to 30.0 percent of chromium, from 15.0 percent to 30 percent of cobalt, from 1.5 percent to 10.0 percent of tungsten, from 2.5 percent to 7.5 percent of titanium and from 2.75 percent to 5.0 percent of aluminum, the alloy being capable of withstanding an applied stress of thirty five thousand pounds per square inch at 1500 F. for a time in excess of two hundred hours continuously, without rupture.

6. A nickel base alloy containing from 19.0 percent to 22.0 percent of chromium, from 14.0 percent to 16.0 percent of cobalt, from 2.75 percent to 3.25 percent of metal of the class consisting of titanium and zirconium, from 3.5 percent to 4.5 percent of metal of the class consisting of molybdenum and tungsten, from 2.75 percent to 3.25 percent of aluminum, iron up to 5.0 percent, and minor amounts of carbon and sulfur, the balance being substantially nickel, and the alloy being capable of withstanding an applied stress of thirty five thousand pounds per square inch at 1500 F. for a time in excess of two hundred hours continuously, without rupture.

7. A nickel base alloy containing about 19.5 percent of chromium, about 14.8 percent of cobalt, about 3.75 percent of molybdenum, about 2.79 percent of titanium, and about 2.94 percent of aluminum, the alloy being capable of withstanding an applied stress of sixty five thousand pounds per square inch at 1350 F. for a time in excess of three hundred hours continuously, without rupture.

8. A nickel base alloy containing about 19.5 percent of chromium, about 14.8 percent of cobalt, about 3.75 percent of molybdenum, about 2.79 percent of titanium, and about 2.94 percent of aluminum, the alloy also containing carbon, sulfur, iron, and manganese but not materially in excess of a total amount of about 1.0 percent, the balance being nickel, and the alloy being capable of withstanding an applied stress of thirty five thousand pounds per square inch at 1500 F. for a time in excess of two hundred hours continuously, without rupture.

References Cited in the file of this patent UNITED STATES PATENTS 2,497,667 Gresham et al Feb. 14, 1950 2,564,498 Nisbet Aug. 14, 1951 2,570,193 Bieber et al. Oct. 9, 1951 FOREIGN PATENTS 607,616 Great Britain Sept. 2, 1948 987,304 France Apr. 11, 1951 

1. A NICKEL BASE ALLOY CONTAINING FROM 15.0 PERCENT TO 30.0 PERCENT OF CHROMIUM, FROM 15.0 PERCENT TO 30.0 PERCENT OF COBALT, FROM 2.75 PERCENT TO 5.0 PERCENT OF ALUMINUM, FROM 2.5 PERCENT TO 7.5 PERCENT OF TITANIUM, THE ALLOY BEING CAPABLE OF WITHSTANDING AN APPLIED STRESS OF THIRTY FIVE THOUSAND POUNDS PER SQUARE INCH AT 1500*F. FOR A TIME IN EXCESS OF TWO HUNDRED HOURS CONTINOUSLY, WITHOUT RUPTURE. 